It is known in the art to apply cardiac leads employing electrodes that transmit electrical signals for three major purposes: mapping, pacing and defibrillating. Each lead type was designed to meet the electrical and mechanical requirements imposed by its intended use and location of operation.
In the beating heart, the intrinsic electrical activity propagates along the HIS-Purkinje intrinsic conductance pathways and between neighboring muscular regions. Changes in localized electrical activity in the form of cellular depolarization cause local contraction of that muscular region. The depolarization wave arrives to different cardiac locations at different delays from the intrinsic or artificial pacemaker. In order to synchronize the delivery of contractility modulating electrical signal to each of the localized cardiac regions, the precise timing of localized depolarization at that same location is needed. An example for such contractility-enhancing signal is the non-excitatory signal described in WO 97/25098, the description of which is incorporated herein by reference.
The catheter known in the art to be used for electro-physiological (EP) mapping of the cardiac muscle generally senses the localized cardiac electrical activity at the point of contact between the electrode and the muscle to detect regions of abnormal activity. Generally, a small surface area characterizes the electrodes of said catheter to achieve reliable sensing. Among the different catheters, some are used for mapping the endocardial walls of the cardiac chambers; they are large in diameter, generally 2.5-3.0 mm, and have only a few electrodes at the tip of the catheter, whose position can be controlled by external means. Different parts of the cardiac chamber (atrium or ventricle) wall can be accessed sequentially, and their localized electrical activity mapped. Other mapping catheters, which are used to access the epicardial wall, via the coronary venous system, are very thin, generally less than 1 mm in diameter, and therefore enables access to the small branches of the vasculature and employ small, multiple electrodes distributed along the length of the catheter. Generally, the vessel's diameter decreases toward the branches, from the ostium of the coronary sinus, via the great cardiac vein to less than 30 μm at the venules.
The art deals, e.g., in U.S. Pat. No. 5,711,298, with the high resolution mapping of localized cardiac electrical activity through the coronary vasculature, and employs catheters with a plurality of sensing electrodes distributed along it, or guidewire stem with inter-electrode distance of less than 2 mm. The shaft of the catheter is formed of a plurality of insulated conductors, braided or wound into an elongated tubular shape with a central lumen and an external sleeve covering the entire shaft. The diameter of the shaft is preferably less than 0.75 mm. These electrodes are small, designed for sensing of electrical activity and they are not designed for the delivery of electrical energy to the tissue. Similarly, the shaft of the catheter is not designed for long term implant and high fatigue life.
Prior art methods for the delivery of electrical energy into the cardiac muscle include pacing leads and defibrillator leads. Both types of leads do not provide means for efficient energy delivery at multiple locations nor provide non-excitatory electric fields at localized locations in the cardiac chamber. The unipolar pacing lead has a small signal delivery tip (1-10 mm2) through which the electrical energy is sensed from, and delivered into, a single localized region of the tissue generating a propagating action potential. The bipolar pacing lead has an additional ring electrode that enables localized sensing and signal delivery. However, similar to the unipolar lead, these electrodes and leads are designed for energy delivery and sensing from a single and small localized region of the cardiac muscle. The position of the lead is normally in one of the cardiac chambers, although some pacing leads can be used for cardiac stimulation through the coronary sinus or cardiac veins. There are also other forms of pacing leads, for example epicardial pacing leads that are attached to the epicardial wall of the heart, capable of performing similar functions. A typical pacing pulse is a sharp, narrow electrical pulse with a 0.1 to 1.5 msec duration, a total discharge of 0.1-50 μC and an energy of about 100 μJ. It does not require that the electric capacitance of the electrode be high, because of the short duration of the signal, and a value of less than 100 μF, which is the value used in the art, is sufficient. It is also required that the electrode will have a short recovery time to enable it to act as a sensor within a few milliseconds after delivering the signal. The electric field applied, through high impedance, is local and generally low. U.S. Pat. No. 4,848,352 discloses a method and device for cardiac pacing and sensing which uses a plurality of electrodes carried by a lead.
The defibrillator lead and electrodes are designed for the delivery of a small consecutive number of high energy pulses to the cardiac muscle upon demand. This energy delivery is to the whole mass of the chamber, and thus it is not localized. The defibrillator electrode is not used for the sensing of the localized electrical activity, and separate sensing electrodes are needed. The additional sensing electrode(s) are situated on the same defibrillator lead, or on a pacing lead that is positioned elsewhere in the heart. Both methods of electrical signal sensing are not adequate for signal detection at the vicinity of a defibrillator electrode. U.S. Pat. No. 5,545,205 discloses a unitary intravascular defibrillating lead which is part of an apparatus which includes a cardioversion circuit, and carries a distal and proximal spring electrode, displaced at such distance from one another that defibrillating shock is affected through a field including the interventricular septum and left ventricular free wall.
The use of a multi-chamber lead or catheter through the GCV for pacing, whether combined or not combined with non-excitatory signal delivery, has not been described in the art.
What has been needed is a method and system for the precise delivery of multiple electrical signals to a plurality of locations on the cardiac muscle, each of which is synchronized, to the locally sensed intrinsic electrical activity.
The timing and characteristics of an electrical field that modifies the contractility of the heart and the sensing required for controlling the delivery of the signal required, are entirely different from any signal applied to the heart for pacing or defibrillating. Subsequently, there is no lead known in the field that fulfills the combination of requirements of a lead employing electrodes that deliver a non-excitatory signal in the appropriate timing and location. Such a lead and such electrodes are the objects of this invention.
This invention has the purpose of providing a device, in particular a multi-electrode lead, to deliver a non-excitatory signal.
It is another purpose of this invention to provide a device to deliver such a signal synchronized with the local intrinsic excitatory signal of the heart.
It is another purpose of this invention to provide a device that is sufficiently thin as to be inserted transvenously into the distal veins of the Venous system of the heart to deliver such a signal to specific locations of the cardiac muscle.
It is another aim of the present invention to provide a lead adapted for being implanted onto the epicardial surface of the heart using any suitable method of implantation.
It is a further purpose of this invention to provide a lead employing electrodes that are small in surface area to provide reliable local signal delivery and sensing, and at the same time, large enough to be able to deliver, through low impedance, electrical pulses whose energy is higher than that of the pacing pulses.
It is a further purpose of this invention to provide a lead employing electrodes that are small in surface area to provide reliable signal delivery and sensing at multiple locations.
It is a further purpose of this invention to provide a lead employing electrodes which have low impedance, deliver higher energy than pacing energy, but are still biostable for long term implantation.
It is a still further purpose of this invention to provide a lead employing electrodes that deliver a signal of duration determined by the duration of the refractory period.
It is yet another purpose of this invention to provide a lead, primarily intended for such non-excitatory stimulation though capable of performing pacing and defibrillating functions.
It is yet another purpose of this invention to provide a lead, primarily intended for such non-excitatory stimulation though capable of performing pacing and defibrillating functions separately or in combination.
It is still a further object of tie invention to provide a method for applying non-excitatory stimuli to an organ or body cavity.
Other purposes and advantages of the invention will appear as the description proceeds.